The present invention relates to a method of and to an apparatus for manipulating sheets in paper processing plants or the like, especially for manipulating layers or stacks of paper sheets on their way to a packing machine. More particularly, the invention relates to improvements in apparatus for transporting layers or stacks of sheets to a packing or other processing machine in such a way that fluctuations in the rate of delivery of stacks to the apparatus are compensated for before the stacks reach the processing machine so that the rate of admission of stacks into the processing machine invariably conforms to the operating speed of the processing machine and the apparatus compensates for eventual pronounced or less pronounced fluctuations of the rate of admission of stacks thereto, for example, as a result of intermittent delivery of groups of stacks and/or as a result of segregation of unsatisfactory stacks from the remaining stacks.
It is already known to intermittently deliver groups of abutting or closely adjacent stacks to a station which is disposed between the stack forming unit and the processing machine, and to thereupon singularize the stacks of such groups so as to ensure that the processing machine receives properly spaced-apart stacks at a desired rate, namely at a rate conforming to the momentary requirements of the processing machine. To this end, a first conveyor receives groups of stacks from a second conveyor at regular or irregular intervals and is designed to ensure that one outermost stack of the freshly delivered group is moved into abutment with one outermost stack of the previously delivered group. Thus, the first conveyor invariably supports a series of abutting stacks and cooperates with a third (singularizing) conveyor which removes or receives from the first conveyor discrete stacks at the rate which conforms to the then prevailing speed of the processing machine. Reference may be had to the commonly owned copending patent application Ser. No. 374,939 filed May 5, 1982 by Aykut et al., now U.S. Pat. No. 4,518,075 granted May 21, 1985.
U.S. Pat. No. 4,230,218 discloses a modified apparatus for transporting stacks of paper sheets or the like wherein a belt conveyor is driven at a constant speed and cooperates with a belt run having upper and lower belts which are disposed in front of and partially overlap the belt conveyor. The belt run is driven intermittently at a speed varying between zero and a speed exceeding the constant speed of the belt conveyor. The upper and lower belts of the belt run clamp the stacks of paper sheets therebetween and advance the clamped stacks at an elevated speed so as to move the foremost stack into abutment with the last stack on the belt conveyor. The latter cooperates with a singularizing conveyor which converts the group of abutting stacks into a series of discrete stacks advancing toward a packing or other processing machine. The mutual spacing of singularized stacks corresponds to (i.e., it is a function of) the operating speed of the processing machine.
The apparatus of the aforementioned copending application Ser. No. 374,939 deviates from the patented apparatus because it comprises an intermittently driven transverse conveyor preceding a continuously driven gathering conveyor which is followed by the singularizing conveyor. The gathering conveyor comprises several discrete endless bands which are disposed one after the other, as considered in the direction of transport of stacks toward the singularizing conveyor. Each discrete band can be accelerated individually from a lower basic speed to a higher speed so as to ensure that the trailing stack or stacks can be moved nearer to the preceding stacks ahead of the singularizing conveyor. This ensures that the gathering conveyor can accumulate a group of abutting stacks, the foremost one of which advances into the range of the singularizing conveyor whose operation is synchronized with that of the processing machine. In other words, the bands of the gathering conveyor cooperate to compensate for eventual irregularities in the rate of delivery of stacks by the transverse conveyor in order to enable the singularizing conveyor to invariably establish gaps of desired width between the series of discrete stacks.
The aforediscussed apparatus operate satisfactorily under normal circumstances, i.e., the processing machine (normally a packing machine) can receive discrete stacks at a desired rate which enables it to perform the desired operations even if the operating speed varies for any one of a variety of reasons. However, such apparatus cannot ensure predictable delivery of stacks or analogous accumulations of paper sheets or the like to a processing machine if certain stacks must be segregated from other stacks because they exhibit defects or for any other reason. This creates pronounced gaps in the stream of stacks which are delivered to the gathering conveyor so that it would be necessary to effect extremely high acceleration of discrete bands forming part of the gathering conveyor with attendant danger of deformation of the stacks. Alternatively, the path along which the stacks following one or more segregated stacks must be advanced at a higher than average speed is much longer than practical or warranted in a production line for the packing of reams of paper sheets or for the making of steno pads, exercise books and analogous stationery products. In the absence of such undertakings, the processing machine cannot receive stacks at a desired rate; this can cause damage to the processing machine (for example, a packing machine) and/or destruction of stacks which are delivered to the processing machine at inopportune times.
In accordance with another prior proposal which is disclosed in German Offenlegungsschrift No. 27 40 175, the speed of the motor which drives the packing machine is regulated so as to account for the absence of regular or predictable delivery of commodities (biscuits or the like) thereto. This is not a satisfactory solution in production lines which turn out large numbers of packed or otherwise processed goods per unit of time. First of all, repeated acceleration and deceleration of all moving parts in a packing machine for reams of paper sheets or the like entails pronounced wear and greatly reduces the useful life of such machines. Moreover, the stresses upon repeatedly accelerated and decelerated parts are so pronounced that they cannot be accepted in production lines for the making of stationery products or the like which are turned out at the presently required rates.